To build the Hubble diagram of QSOs, two quantities are required: the distance modulus and the redshift for a statistical significant sample of sources. The distance modulus is obtained from the luminosity distance (e.g., [1]}, [2]}) defined as:
\(\log d_{\rm L} = \frac{\left[\log F_{\rm X} -\beta -\gamma (\log F_{\rm UV}+27.5) \right]}{2(\gamma -1)}-\frac{1}{2}\log (4\pi ) + 28.5,\) 
